/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.util;

import org.springframework.lang.Nullable;

import java.lang.reflect.GenericArrayType;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.WildcardType;

/**
 * Utility to work with Java 5 generic type parameters.
 * Mainly for internal use within the framework.
 *
 * @author Ramnivas Laddad
 * @author Juergen Hoeller
 * @author Chris Beams
 * @since 2.0.7
 */
public abstract class TypeUtils
{

    /**
     * Check if the right-hand side type may be assigned to the left-hand side
     * type following the Java generics rules.
     *
     * @param lhsType the target type
     * @param rhsType the value type that should be assigned to the target type
     * @return true if rhs is assignable to lhs
     */
    public static boolean isAssignable(Type lhsType, Type rhsType)
    {
        Assert.notNull(lhsType, "Left-hand side type must not be null");
        Assert.notNull(rhsType, "Right-hand side type must not be null");

        // all types are assignable to themselves and to class Object
        if (lhsType.equals(rhsType) || Object.class == lhsType)
        {
            return true;
        }

        if (lhsType instanceof Class)
        {
            Class<?> lhsClass = (Class<?>) lhsType;

            // just comparing two classes
            if (rhsType instanceof Class)
            {
                return ClassUtils.isAssignable(lhsClass, (Class<?>) rhsType);
            }

            if (rhsType instanceof ParameterizedType)
            {
                Type rhsRaw = ((ParameterizedType) rhsType).getRawType();

                // a parameterized type is always assignable to its raw class type
                if (rhsRaw instanceof Class)
                {
                    return ClassUtils.isAssignable(lhsClass, (Class<?>) rhsRaw);
                }
            }
            else if (lhsClass.isArray() && rhsType instanceof GenericArrayType)
            {
                Type rhsComponent = ((GenericArrayType) rhsType).getGenericComponentType();

                return isAssignable(lhsClass.getComponentType(), rhsComponent);
            }
        }

        // parameterized types are only assignable to other parameterized types and class types
        if (lhsType instanceof ParameterizedType)
        {
            if (rhsType instanceof Class)
            {
                Type lhsRaw = ((ParameterizedType) lhsType).getRawType();

                if (lhsRaw instanceof Class)
                {
                    return ClassUtils.isAssignable((Class<?>) lhsRaw, (Class<?>) rhsType);
                }
            }
            else if (rhsType instanceof ParameterizedType)
            {
                return isAssignable((ParameterizedType) lhsType, (ParameterizedType) rhsType);
            }
        }

        if (lhsType instanceof GenericArrayType)
        {
            Type lhsComponent = ((GenericArrayType) lhsType).getGenericComponentType();

            if (rhsType instanceof Class)
            {
                Class<?> rhsClass = (Class<?>) rhsType;

                if (rhsClass.isArray())
                {
                    return isAssignable(lhsComponent, rhsClass.getComponentType());
                }
            }
            else if (rhsType instanceof GenericArrayType)
            {
                Type rhsComponent = ((GenericArrayType) rhsType).getGenericComponentType();

                return isAssignable(lhsComponent, rhsComponent);
            }
        }

        if (lhsType instanceof WildcardType)
        {
            return isAssignable((WildcardType) lhsType, rhsType);
        }

        return false;
    }

    private static boolean isAssignable(ParameterizedType lhsType, ParameterizedType rhsType)
    {
        if (lhsType.equals(rhsType))
        {
            return true;
        }

        Type[] lhsTypeArguments = lhsType.getActualTypeArguments();
        Type[] rhsTypeArguments = rhsType.getActualTypeArguments();

        if (lhsTypeArguments.length != rhsTypeArguments.length)
        {
            return false;
        }

        for (int size = lhsTypeArguments.length, i = 0; i < size; ++i)
        {
            Type lhsArg = lhsTypeArguments[i];
            Type rhsArg = rhsTypeArguments[i];

            if (!lhsArg.equals(rhsArg) && !(lhsArg instanceof WildcardType && isAssignable((WildcardType) lhsArg, rhsArg)))
            {
                return false;
            }
        }

        return true;
    }

    private static boolean isAssignable(WildcardType lhsType, Type rhsType)
    {
        Type[] lUpperBounds = lhsType.getUpperBounds();

        // supply the implicit upper bound if none are specified
        if (lUpperBounds.length == 0)
        {
            lUpperBounds = new Type[]{Object.class};
        }

        Type[] lLowerBounds = lhsType.getLowerBounds();

        // supply the implicit lower bound if none are specified
        if (lLowerBounds.length == 0)
        {
            lLowerBounds = new Type[]{null};
        }

        if (rhsType instanceof WildcardType)
        {
            // both the upper and lower bounds of the right-hand side must be
            // completely enclosed in the upper and lower bounds of the left-
            // hand side.
            WildcardType rhsWcType    = (WildcardType) rhsType;
            Type[]       rUpperBounds = rhsWcType.getUpperBounds();

            if (rUpperBounds.length == 0)
            {
                rUpperBounds = new Type[]{Object.class};
            }

            Type[] rLowerBounds = rhsWcType.getLowerBounds();

            if (rLowerBounds.length == 0)
            {
                rLowerBounds = new Type[]{null};
            }

            for (Type lBound : lUpperBounds)
            {
                for (Type rBound : rUpperBounds)
                {
                    if (!isAssignableBound(lBound, rBound))
                    {
                        return false;
                    }
                }

                for (Type rBound : rLowerBounds)
                {
                    if (!isAssignableBound(lBound, rBound))
                    {
                        return false;
                    }
                }
            }

            for (Type lBound : lLowerBounds)
            {
                for (Type rBound : rUpperBounds)
                {
                    if (!isAssignableBound(rBound, lBound))
                    {
                        return false;
                    }
                }

                for (Type rBound : rLowerBounds)
                {
                    if (!isAssignableBound(rBound, lBound))
                    {
                        return false;
                    }
                }
            }
        }
        else
        {
            for (Type lBound : lUpperBounds)
            {
                if (!isAssignableBound(lBound, rhsType))
                {
                    return false;
                }
            }

            for (Type lBound : lLowerBounds)
            {
                if (!isAssignableBound(rhsType, lBound))
                {
                    return false;
                }
            }
        }

        return true;
    }

    public static boolean isAssignableBound(@Nullable Type lhsType, @Nullable Type rhsType)
    {
        if (rhsType == null)
        {
            return true;
        }
        if (lhsType == null)
        {
            return false;
        }
        return isAssignable(lhsType, rhsType);
    }

}
